Craftsman with 17 OHV won't start, backfires

[Mithril]

Greeting esteemed mower owners,

I have a 15 year old Craftsman tractor with a 17HP OHV Briggs and Stratton engine that won't start but occasionlly backfires. When I took it out of mothballs after a long winter the engine started right up and ran well. Then after mowing the lawn it started have a problem, it would crank and crank and didn't want to start even choked but eventually would fire up. Once warmed up it would run great. Then the other day I was running the tractor and engaged the mower blades and it stalled and would not start again. Here's what I've done so far:

1) Checked flywheel key and it's OK
2) Engine has spark
3) checked after-fire solonoid and it works
4) replaced spark plug
5) checked compression at 105PSI, not sure if this is a problem or not, have leak down tester on order to do proper test.
6) Replaced fuel filter
7) Adjusted valves, they were pretty much OK anyway.
8) engine will fire with starter fluid but quickly dies.

When it first happened I was leaning towards a broken key since it seemed that the problem occurred when I engaged the blades, but there's nothing wrong with it. I have gaskets on order to do a carb cleaning.

Am I missing anything?

Thanks
-Bob

 

[EngineMan]

When you say it backfires, do you mean from the carb or from the exhaust, you also didn't say if you check the choke, is it performing correctly.

 

[Mithril]

It backfires mostly from the exhaust but at least once backfired from the carb. The choke seems to be working well, When I put the lever in the choke position the choke flap closes.

Cheers
-Bob

 

[EngineMan]

It backfires mostly from the exhaust but at least once backfired from the carb. The choke seems to be working well, When I put the lever in the choke position the choke flap closes.

Cheers
-Bob

If its out of exhaust that is too much fuel getting into exhaust (unburned) if its out of inlet that could be lean mix or valve still remaining open under power stroke.

Are you sure you have a good spark, also give a few turns with choke on, and then open the choke (leave open) and then try to start it.

 

[Mithril]

If its out of exhaust that is too much fuel getting into exhaust (unburned) if its out of inlet that could be lean mix or valve still remaining open under power stroke.

Are you sure you have a good spark.

Yeah, I used an inline spark tester and I see consistent spark, it's yellow, but that may be how the tester displays it.

I removed the carb and pulled the bowl, there was rust on the bottom of the bowl otherwise the carb looks clean.

-Bob

 

[EngineMan]

You say "Then the other day I was running the tractor and engaged the mower blades and it stalled and would not start again."
that should say its the coil side (s/switch), see if you can remove the kill wire (making sure its not going to ground) and then see if engine will start, remember if it does start up you will have to kill engine by turning off the fuel....!

 

[Mithril]

You say "Then the other day I was running the tractor and engaged the mower blades and it stalled and would not start again."
that should say its the coil side (s/switch), see if you can remove the kill wire (making sure its not going to ground) and then see if engine will start, remember if it does start up you will have to kill engine by turning off the fuel....!

I thought of the kill switch but wouldn't that prevent me from seeing spark?

 

[EngineMan]

I thought of the kill switch but wouldn't that prevent me from seeing spark?

You may still see a little spark but that may not be good to start it (if there is path to ground)

 

[Mithril]

You may still see a little spark but that may not be good to start it (if there is path to ground)

It must have been something in the carb. I removed it, took off the bowl and found flakes of rust in it. I removed them, sprayed all the orifices with carb cleaner, let it dry then reassembled it and viola, it starts and runs like new. Carb must have sucked up some gunk and the blade engagement was a coincidence. The old gaskets are holding up, no leaks in the bowl o-ring nor in the solonoid gasket.

I guess I have $70 worth of parts coming I may not need.

-Bob

 

[EngineMan]

It was lean then......just to say WELL DONE you got there...:thumbsup: